Multiple antisera, containing antibodies directed to a wide range of sperm-specific GP antigens with respect to species-specificity, antigen locations and antigenic specificity, will be developed in male GP and male rabbits. The effects of IgG and Fab isolated from these antisera on GP sperm in (a) capacitation, (b) acrosome reaction, (c) attachment and penetration of the zona pellucida and (d) attachment and fusion with zona-free GP ova in the absence of sperm agglutination will be determined in vitro by light and electron microscopy. Thus, this study will determine conclusively whether in GP, antibodies to sperm-specific antigen(s) can inhibit the distinctive events of prefertilization ad fertilization of sperm in vitro. Should inhibition of any of the steps be observed, we will determine (1) the dose of antibody required to inhibit; (2) the location of sperm antigen by immunofluorescence and immunoelectron microscopy using sperm at different stages of prefertilization and fertilization; (3) the species-specificity of the inhibition and (4) whether univalent (Fab) and/or bivalent (IgG) antibody is required in the inhibition. As a long-term goal, and not included as part of the present proposal, the relevant antigen(s) will be (1) isolated, precisely localized on or in the sperm, biochemically characterized, and used in the immunologic induction of infertilization in female animals; and (2) used as markers to study prefertilization and fertilization events in vitro. Finally, a similar on the human system in vitro will then be initiated.